1. Field of the Invention
The present invention relates in general to valve operating devices of internal combustion engine, and more particularly to the valve operating devices of a type wherein the valve lifting is controlled in accordance with the operating condition of the engine.
2. Description of Related Art
In order to clarify the task of the present invention, one related valve operating device of the above-mentioned type will be briefly described in the following, which is shown in Japanese Utility Model First Provisional Publication 6-73301.
In the device, low speed cams used for all operation ranges of the engine are mounted on a cam shaft. Each low speed cam slidably contacts a main rocker arm to actuate intake or exhaust valves. The main rocker arm is pivotally mounted on a rocker shaft. Beside the low speed cam, medium speed and high speed cams are also mounted on the cam shaft, which are used for middle and high speed operation ranges of the engine respectively. The medium and high speed cams slidably contact respective sub-locker arms which are pivotally mounted on the rocker shaft beside the above-mentioned locker arm. During operation of the engine, the two sub-rocker arms are selectively fixed to the main locker arm by means of a switching mechanism.
The switching mechanism comprises generally two connecting levers which are pivotally connected to the main rocker arm. One of the connecting levers is operated for fixing one of sub-rocker arms to the main rocker arm, and the other connecting lever is operated for fixing the other sub-rocker arm to the main rocker arm. Thus, when one of the sub-rocker arms is fixed to the main rocker arm, these two rocker arms constitute a single unit which is pivotally actuated by selected one of the medium and high speed cams that actually contacts a cam follower of the sub-rocker arm. Thus, in this case, the opening/closing operation of the intake or exhaust valves is timed by the selected one of the medium and high speed cams.
In the multi-cylinder internal combustion engines, for reducing a pumping loss at the time of a low load operation, various measures have been hitherto proposed and put into practical use. One of them is shown in Japanese Patent First Provisional Publication 5-248215. In the pumping loss reduction measure of this publication, the intake and/or exhaust valves of given cylinders are made inoperative under a low load operation of the engine. For making the intake and exhaust valves inoperative, the publication discloses an arrangement wherein a sub-rocker arm can be selectively fixed to a rocker shaft to which a main rocker arm for operating the intake or exhaust valves is fixed and wherein a hydraulically actuated connecting plunger for fixing the two rocker arms is slidably received in a receiving hole formed in the rocker shaft. When the connecting plunger is disengaged from the sub-rocker arm, the sub-rocker arm becomes pivotal relative to the main rocker arm, and thus the pivoting movement of the sub-rocker arm induced by rotation of an associated cam does not induce the pivoting movement of the main rocker arm. Thus, in this case, the intake valves and/or the exhaust valves of the given cylinders are forced to take their rest condition even under operation of the engine, which reduces the pumping loss of the engine. In the disclosed measure of the publication, in order to disengage the connecting plunger from the sub-rocker arm, it is needed to stop feeding of hydraulic pressure to a hydraulic work chamber for the connecting plunger. Upon stopping of the pressure feeding, the connecting plunger is retracted into the receiving hole of the rocker shaft due to a biasing force of a coil spring.
In the arrangement of the publication 5-248215, for engaging the connecting plunger with the sub-rocker arm, it is needed to feed the hydraulic pressure to the hydraulic work chamber for the connecting plunger. However, due to inherent construction of the arrangement, feeding of sufficient hydraulic pressure to the hydraulic work chamber is not quickly carried out, especially in winter. Thus, upon restarting of the engine, it tends to occur that the intake and/or exhaust valves of the certain cylinders keep the rest condition for a certain time, which induces a non-smoothed engine starting.
It is therefore an object of the present invention to provide a valve operating device of an internal combustion engine, which can provide the engine with a smoothed engine starting even when the engine was subjected to the pumping loss reduction operation before engine stopping.
According to a first aspect of the present invention, there is provided a valve operating device of an internal combustion engine, which comprises low and high speed cams coaxially disposed on a cam shaft, the low speed cam having a lobe that is lower than that of the high speed cam; a main rocker arm pivotally supported by a rocker shaft and operatively contacting an intake or exhaust valve of the engine to actuate the same; first and second sub-rocker arms pivotally supported by the main rocker arm and pivotally actuated by the low and high speed cams respectively; a connecting member supported by the main rocker arm, the connecting member comprising first and second engaging portions which are respectively engageable with first and second engaged portions defined by the first and second sub-rocker arms, so that upon engagement of the first engaging portion with the first engaged portion, the first sub-rocker arm and the main rocker arm become fixed to each other to pivot about the rocker shaft like a single unit, and upon engagement of the second engaging portion with the second engaged portion, the second sub-rocker arm and the main rocker arm become fixed to each other to pivot about the rocker shaft like a single unit; a hydraulically actuating mechanism comprising first and second hydraulic work chambers, the mechanism inducing the engagement between the first engaging portion and the first engaged portion upon discharge of hydraulic fluid from the first work chamber and inducing a disengagement between the first engaging portion and the first engaged portion upon feeding of the hydraulic fluid into the first work chamber, and the mechanism selectively inducing the engagement or disengagement between the second engaging portion and the second engaged portion in accordance with a pressure of hydraulic fluid fed to the second work chamber; a hydraulic pressure producing unit that feeds the first and second work chambers with hydraulic pressure respectively; and a control unit that, in accordance with operation condition of the engine, controls the hydraulic pressure producing unit, so that the hydraulically actuating mechanism has at least first, second and third operation modes, the first mode being a mode wherein disengagement takes place both between the first engaging portion and the first engaged portion and between the second engaging portion and the second disengaged portion, the second mode being a mode wherein engagement takes place between the first engaging portion and the first engaged portion and disengagement takes place between the second engaging portion and the second engaged portion, the third mode being a mode wherein engagement takes place both between the first engaging portion and the first engaged portion and between the second engaging portion and the second engaged potion.
According to a second aspect of the present invention, there is provided a valve operating device of an internal combustion engine, which comprises a plurality of cams coaxially disposed on a cam shaft, one of the cam being a low speed cam; a rocker arm pivotally supported by a rocker shaft and operatively contacting an intake or exhaust valve of the engine to actuate the same; a sub-rocker arm pivotally supported by the rocker shaft and pivotally actuated by the low speed cam; a connecting member supported by the main rocker arm, the connecting member having both a first condition wherein the sub-rocker arm and the main rocker arm are fixed to each other to constitute a single unit and a second condition wherein the sub-rocker arm and the main rocker arm are disengaged from each other; a hydraulically actuating mechanism including a hydraulic work chamber, the mechanism inducing the first condition of the connecting member upon discharge of hydraulic fluid from the work chamber and inducing the second condition upon feeding of hydraulic fluid to the work chamber; and a control unit that causes the hydraulically actuating mechanism to induce the first condition of the connecting member when the engine stops.
According to a third aspect of the present invention, there is provided a valve operating device of an internal combustion engine, which comprises at least one cam disposed on a cam shaft; a rocker arm pivotally supported by a rocker shaft and operatively contacting an intake or exhaust valve of a cylinder of the engine to actuate the same; a sub-rocker arm pivotally supported by the main rocker arm and pivotally actuated by the cam; a connecting member supported by the main rocker arm, the connecting member having both a first condition wherein the sub-rocker arm and the main rocker arm are fixed to each other to pivot about the rocker shaft like a single unit and a second condition wherein the sub-rocker arm and the main rocker arm are disengaged from each other to fail to transmit a pivotal movement of the sub-rocker arm induced by rotation of the cam to the main rocker arm thereby to stop operation of the intake or exhaust valve; a hydraulically actuating mechanism including a hydraulic work chamber, the mechanism inducing the first condition of the connecting member upon discharge of hydraulic fluid from the work chamber and inducing the second condition upon feeding of hydraulic fluid to the work chamber; and a control unit that causes the hydraulic actuating mechanism to induce the first condition of the connecting member when the engine stops.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.